This invention relates to a control system for evaporated fuel in a supercharged internal combustion engine, and more particularly to an improvement of evaporated fuel supply passages between a fuel reservoir and an air intake means.
In Published Japanese patent application No. 57-143155, there is disclosed an internal combustion engine having an electronic fuel injection system, which includes an example of the prior art control system for evaporated fuel as illustrated in FIGS. 1(A) and 1(B).
The prior art control system for evaporated fuel in FIG. 1(A) comprises an air intake passage means including an air cleaner 1 to introduce air, an air flow meter 2 to meter the flow rate of the air passing therethrough, a supercharging impeller 3 which is accomodated in a supercharger housing 4 and rotated by an exhaust gas impeller (not shown) driven by exhaust pressure, a throttle valve 5 housed in a throttle chamber 6 to receive the air pressurized by the supercharging impeller 3 and an intake manifold 7 to pass the air to each combustion chamber of an engine main portion 8.
The prior art control system further comprises an evaporated fuel supply passage means including a fuel tank 9 having an air chamber 10 and a canister 11 filled with adsorbent such as activated carbon for a reservoir 12, wherein the fuel tank 9 is communicated with the canister 11 through a passage 14 having a check valve 13 therein. The canister 11 is adapted to accomodate temporarily through adsorption the evaporated fuel produced in and sent from the fuel tank 9, for example after the stop of the engine operation.
The canister 11 comprising the reservoir 12 is communicated with the intake manifold 7 at a portion downstream of the throttle valve 5 through a first evaporated fuel supply passage 15.
Disposed at the end of the first evaporated fuel supply passage 15 above the reservoir 12 is a first purge control valve 16 to open and close controllably the first evaporated fuel passage 15. The first purge control valve 16 may be of the type operational in a manner to be open during the throttling operation wherein a vacuum or negative pressure is created around or downstream of the throttle valve 5 in the air intake passage means.
The structure and operation of the first purge control valve 16 is set forth in detail hereinafter referring to FIG. 1(B).
The first purge control valve 16 comprises an upper extension of the canister 11 partially defining a plenum 16A, a diaphragm 16B defining the plenum 16A together with the upper extension of the canister 11 and separating the plenum 16A from the reservoir 12 and a valve body 16C integrally connected to the central portion of the diaphragm 16B and being positioned adjacent the opening 15A with an orifice of the first evaporated fuel supply passage 15.
The plenum 16A is communicated with the throttle chamber 6 through a passage 17 and supplied with a vacuum or negative pressure (VC negative pressure) around the throttle valve 5. Accordingly, the first purge control valve 16 is operated in correspondence with the vacuum or negative pressure around the throttle valve 5 such that the diaphragm 16B moves upwards with reference to the drawing when the plenum 16A is exposed to a higher vacuum during the lower and medium load ranges or throttling operation of the engine. The upward movement of the diaphragm 16B causes the valve body 16C integrally connected to the diaphragm 16B to open an opening or orifice 15A of the first evaporated fuel supply passage 15 so that the passage 15 is communicated with the reservoir 12.
Additionaly connected to the canister 11 above the reservoir 12 is a second evaporated fuel supply passage 19 which communicates the interior of the canister 11 comprising the reservoir 12 with an intake passage or duct 18 upstream of the supercharging impeller 3, in other words between the air flow meter 2 and the supercharging impeller 3. The air flow meter 2 and other members upstream from the supercharging impeller 3 provide air-flow resistance which produces a negative pressure in the intake duct 18. The second evaporated fuel supply passage 19 at the end thereof adjacent the canister 11 is provided with an orifice 20 of a predetermined diameter.
Formed on the lower side of the canister 11 is an opening 21a for drawing the ambient air, and a filter or air cleaner 21b is provided adjacent the opening 21a.
In operation, when the throttle valve 5 is controlled during the lower or medium load range of the prior art engine so that a vacuum or negative pressure prevails around the throttle valve 5 in the air intake passage means, the first purge control valve 16 is opened so that the first evaporated fuel supply passage 15 provides flow communication between the canister 11 and the intake manifold 7 as mentioned above.
Accordingly, the vacuum or negative pressure in the manifold 7 downstream of the intake valve 5 is applied to the canister 11 comprising the reservior 12 through the first evaporated fuel supply passage 15. The vacuum or negative pressure applied to the canister 11 through the first evaporated fuel supply passage 15 causes the evaporated fuel absorbed in the reservoir 12 in the canister 11 to go out of the reservoir 12 together with air which has passed through the filter 21b. The mixture of the evaporated fuel and air is introduced into the intake manifold 7 through the first evaporated fuel supply passage 15 and then into each combustion chamber of the engine main portion 8 for combustion process. The evaporated fuel is thus purged from the reservoir 12 in the canister 11.
The canister 11 is communicated not only with the intake manifold 7 but also with the intake duct 18 between the supercharging impeller 3 and the air flow meter 2 through the second evaporated fuel supply passage 19 as mentioned above. Since the second evaporated fuel supply passage 19 is always open, the negative pressure in the intake duct 18 is always applied to the reservoir 12 in the canister 11. However, the flow rate of air during the low or medium load operation is small, and therefore the vacuum or negative pressure in the intake duct 18 is low or weak, so that only a limited amount of the evaporated fuel is purged through the second evaporated fuel supply passage 19. Consequently, it should be noted that almost all of the evaporated fuel is purged through the first evaporated fuel supply passage 15.
On the other hand, when the throttle valve 5 is controlled so as to be substantially in a fully opened condition during the high load range of the prior art engine, the supercharging impeller 3 pressurizes the intake manifold 7, so that the pressure in the intake manifold 7 and the throttle chamber 6 becomes so positive as to force the valve body 16C of the first purge control valve 16 against the end of the first evaporated fuel supply passage 15, thereby closing the first purge control valve 16. Therefore, the evaporated gas is prevented from flowing through the first evaporated fuel supply passage 15.
Consequently, it will be noted that only the negative pressure from the intake duct 18 is applied to the reservoir 12 in the canister 11 through the second evaporated fuel supply passage 19. Accordingly, the evaporated fuel adsorbed in the reservoir 12 is drawn into the intake duct 18 through the second evaporated fuel supply passage 19, urged to flow into the intake manifold 7 by the supercharging impeller 3 and then supplied to each combustion chamber of the engine main portion 8 for the combustion process as mentioned previously. In this case, it should be noted that the amount of air flow during the high load operation is so large that an increased amount of the evaporated fuel is purged through the second evaporated fuel supply passage 19.
From the foregoing description, it will be understood that the evaporated fuel of the prior art engine undergoes the combustion process in correspondence with the operation condition of the engine.
However, since the second evaporated fuel supply passage 19 is always open in such a control system for evaporated fuel of the prior art supercharged internal combustion engine, part of the evaporated fuel may be purged to the intake duct 18 through the second evaporated fuel supply passage 19 even when the engine is stopped. This causes a problem that the evaporated fuel purged as mentioned above flows reversely through the air flow meter 2 and the filter 1 and exhausted to the atmosphere. Also, in the operation of such a prior art supercharged internal combustion engine in which the air flow meter 2 is of the hot-wire type, for instance when the throttle valve 5 is suddenly closed, intake pulsations occur in the intake duct 18 because the evaporated fuel is always purged into the intake duct 18. Such intake pulsations would cause the evaporated fuel purged to the intake duct 18 to flow reversely to the air flow meter 2 of the hot-wire type and come into contact with a hot-wire in a heat-generating condition. This would cause the evaporated fuel to burn, thereby burning out the hot-wire.
Accordingly, a primary object by the present invention is to provide a control system for evaporated fuel which prevents securely the evaporated fuel from being exhausted to the atmosphere reversely through the air intake passage in a supercharged internal combustion engine.
Another object of the present invention is to provide a control system for evaporated fuel in a supercharged internal combustion engine which prevents securely the evaporated fuel from being purged from the reservoir therefor when the engine is stopped.
Another object of the present invention is to provide a control system for evaporated fuel which can be applied without failure to a supercharged internal combustion engine having an air flow meter of the hot-wire type.